Recently, such as in plastic waste treatment problem and environmental problem, it is prompted intensive studies for application of polylactic acid resins that is prepared from a vegetable-derived raw material and superior in biodegradability widely as a general-purpose polymer. There are many studies conducted on polylactic acid resin compositions. However, the polylactic acid resin is generally a hard and brittle polymer. For that reason, for use of the homopolymer as it is as a general-purpose polymer in various applications, there are many problems left in individual applications.
In particular, when the polylactic acid resin is to be used as processed into film or sheet, hardness and brittleness of the resin causes a big problem. Various studies are in progress to solve the problem. In particular, widely known are a softening method by addition of a plasticizer such as polyethylene glycol and a method of overcoming brittleness for example by addition of an aliphatic polyester. Combined use of these methods permitted wider use of the polylactic acid. However, the polyethylene glycol, which is used as plasticizer, causes a concern about adverse effect on environment. In addition, there is also a problem that addition of an aliphatic polyester makes the resulting polylactic acid resin opaque.
In addition to the resin modification methods, newly proposed were methods of changing the additive used in the polylactic acid resin to a low-environmental-load material such as vegetable oil-derived component or natural oil-derived component (Patent Documents 1 to 3). These methods are lower in environmental load than traditional methods and improved the heat resistance and the shock resistance of the polylactic acid resin. However, these methods are not those for softening or for prevention of bleeding out (extraction). In these methods, only a vegetable oil-derived component or a natural oil-derived component is blended with the polylactic acid resin. Accordingly, the polylactic acid resin, when processed into film or sheet, does not have a function to prevent bleeding out (extraction) sufficiently.    Patent Document 1: JP-A No. 11-116785    Patent Document 2: JP-A No. 2003-002921    Patent Document 3: JP-A No. 2006-077126